Electronic controls for compression ignition engines are known in the art. Some of those known electronic controls have provided more flexibility and greater control over engine performance and emissions than do mechanical controls. For example, when used in connection with an on-highway truck, some electronic controls provide the capability to program a maximum vehicle speed limit. Maximum vehicle speed typically could only be limited in mechanically controlled engines by matching the maximum engine speed with a specific transmission and differential ratio. Although this mechanical method prevented operators from running faster than the desired speed it did not always permit the engine to run most efficiently.
Electronic controls, however, permit an owner to program a maximum vehicle speed which is then used by the controller to limit power output when the vehicle is traveling faster than that speed. For example, if the maximum vehicle speed is programmed to be 55 MPH, then the electronic control will limit engine power when the vehicle speed exceeds the programmed 55 MPH limit. One such electronic control that incorporates this vehicle speed limiting strategy is the ADEM II controller, readily available on a variety of compression ignition engines from Caterpillar Inc., the assignee of the present patent.
Vehicle speed limiting generally provides improved fuel economy at the expense of reduced speeds and increased trip times. Although the feature is generally favored by fleet owners who want to increase their profits by slowing their drivers down and thereby decreasing the overall operating cost of the vehicle, the feature is sometimes considered an annoyance by drivers who are generally paid by the mile and, therefore, like to increase speed and thereby decrease trip time.
Variations of the vehicle speed limiting feature have been developed to appease both groups. One such variation Is described in U.S. Pat. No. 5,477,827. In that patent a variable vehicle speed limit is described in which the vehicle speed limit may be increased by a fuel economy speed limit adder if the vehicle operator achieves a programmed filtered fuel economy. The philosophy of that device is to provide an incentive for the vehicle operator to maximize fuel economy.
Although the device disclosed in U.S. Pat. No. 5,477,827, might promote fuel efficient driving in some circumstances, it does not work in all driving conditions and does not necessarily promote the most cost effective overall vehicle operation in all instances. For example, there is no way for that control to promote vehicle operation that reduces maintenance costs, another important cost component for fleet managers and owners, which are associated with "hard" driving (i.e., the practice of abruptly controlling the throttle and brake, among other things). Additionally, a driver who drives a city route may not be able to achieve the pre-programmed fuel economy level, not because he is driving inefficiently, but instead because there are many unforeseen signal lights and stop signs which prevent him from achieving the same fuel economy as a vehicle driven on the highway. In those instances a pre-programmed fuel economy level may not promote efficient driving. Also, the device of the '827 patent cannot determine how severely the operator runs the engine and thus cannot account for undue stress the operator may place on the engine, driveline or other engine or vehicle components.
It would be preferable to have a system that promotes efficient overall driving techniques to reduce the overall cost of operating the vehicle.
The present invention is directed toward overcoming one or more of the disadvantages associated with the prior art.